Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.30-2

[Ingo Molnar]

* Ingo Molnar <mingo@xxxxxxx> wrote:

> * Mark_H_Johnson@xxxxxxxxxxxx <Mark_H_Johnson@xxxxxxxxxxxx> wrote:
> 
> >  - echo 0 > /proc/sys/kernel/preempt_wakeup_timing [entered, but
> > display was frozen at this point and did not see newline nor any
> > further output]
> 
> managed to reproduce this on an SMP box but not on an UP box, so i
> think this is SMP related. It definitely happens almost immediately
> after preempt_wakeup_timing is reset - or after preempt_max_timing is
> reset.  (Perhaps a dump_stack() from the wrong place, or something
> like that.)

The lockup was caused by the mutex wakeup being done under the PI lock,
and if a new critical-section latency is reported within try_to_wake_up
then the trylock done there deadlocked. The NMI watchdog triggered but
the printks done there deadlocked as well.

I fixed both the deadlock scenario, and made the NMI printout path more
robust to get the messages out to the console in even such a case. 

The fixes are in the latest (-30-4) patch which can be found at the
usual place:

  http://redhat.com/~mingo/realtime-preempt/  

	Ingo
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